Some posts I have seen suggest a 256 card may be slower than a smaller card. Also keep in mind that Nokia's position on this topic is as follows: Use of any card other than a Nokia memory card will void your warranty on the phone. The largest card they currently are selling fyi is a 64 mg one for over $80.00.
Also the memory I saw at a local Costco was not MMC but rather SD and compact flash which is NOT compatible with the 3650 so be careful to get the right kind of memory.. and from a good name if you don't want to take a chance of screwing up your warranty.
Good luck [/B]